Patent Literature 1 discloses a structure in which a tablet computer (first unit) is detachable from a station (second unit) including a keyboard. More specifically, in Patent Literature 1, the station includes an attachment part to which the tablet computer can be attached. The attachment part has nearly the same width as the lateral part of the station to which the tablet computer is attached. The attachment part is equipped with projections protruding from both lateral ends of the attachment part in a direction perpendicular to the lateral part. The tablet computer is provided, at both ends of its lateral part, with to-be-engaged portions, which can be engaged with the projections of the station.